The present invention relates to an exhaust gas recirculating device used in an internal combustion engine with carburetor of the type for suppressing amount of NOx in the exhaust gas by applying an exhaust gas recirculation. The device is to mix the three items, i.e. fuel, intake air and recirculating exhaust gas to unify the feature of the mixed gas to be supplied to each of the cylinders and thus to improve the distribution characteristics of the mixed gas.
In the conventional system of the exhaust gas recirculation of an internal combustion engine with carburetor, a pipe shaped recirculating exhaust gas passageway is connected to one portion of the intake manifold to recirculate a part of the exhaust gas and said exhaust gas is concentratedly blown out into the mixed gas. In such a system, the recirculating exhaust gas is introduced into the mixed gas with partial concentration so that the mixing of the gases may not become uniform and hence the mixture gas distribution characteristics among each of the cylinders may variate.
The mixed gas has both a gas phase in which the fuel is well vaporized and a liquid phase in which the fuel is not well vaporized and attached on the inner wall of the intake gas passageway and flow down along the wall surface to form a so-called wall stream. This liquid phase portion is difficult to let uniformly distribute among each one of the cylinders mainly owing to the shape of the intake manifold. Accordingly, the air fuel ratio of the mixed gas for each cylinder may fluctuate. This results variation of the combustion and increase of quantity of unburned components in the exhaust gas, such as HC, CO, etc. so that the fuel cost increases by the non-effective utilization of the fuel.
There was a proposal to accelerate the vaporization of the liquid phase fuel by heating the riser portion of the intake manifold. However, the conventional system is not sufficient for realizing good vaporization. Especially the conventional construction of the exhaust gas recirculation system is not suited to use the heat of recirculating exhaust gas for the acceleration of the vaporization of the wall stream of the fuel.